Hydrophilic high density PTFE medical barrier

ABSTRACT

A medical barrier includes a sheet of unsintered substantially unexpanded hydrophilic polytetraflouroethylene (PTFE) polymer material. A PTFE polymer material is described that has a density in a range of about 1.2 gm/cc to about 2.3 gm/cc, and preferably in the range of about 1.45 gm/cc to about 1.55 gm/cc, and having at least one textured surface. In accordance with one embodiment, the sheet has one textured surface and one substantially smooth surface, and has substantially uniform strength in all directions.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of allowed U.S. patentapplication Ser. No. 10/947,066, filed Sep. 21, 2004, now U.S. Pat. No.7,296,998 entitled “HYDROPHILIC HIGH DENSITY PTFE MEDICAL BARRIER,”which claimed the benefit of now-expired U.S. provisional applicationSer. No. 60/505,093, filed Sep. 22, 2003, entitled “HYDROPHILIC HIGHDENSITY PTFE MEDICAL BARRIER,” the disclosures of which applications arehereby incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

Aspects of the present invention relate generally to implantable medicalproducts and more particularly to a hydrophilic high densitypolytetrafluoroethylene (PTFE) medical barrier for use in guided tissueregeneration in the repair of bone defects, and particularly in therepair of alveolar and maxillofacial bone defects.

BACKGROUND

The basic concepts which led to the clinical procedure of guided tissueregeneration were reported by Melcher in 1976 in the Journal ofPeriodontics. This work identified four distinct connective tissue cellphenotypes in the periodontium; the gingival corium, periodontalligament, cementum and bone. Melcher proposed that the healing responsethat occurs after wounding is dependent on the phenotype of cells thatrepopulate the area. With the knowledge that epithelial cells from thegingival soft tissues would proliferate at a faster rate than bone orperiodontal ligament cells, the early efforts at guided tissueregeneration focused on epithelial exclusion by various mechanicalmeans, including the placement of a thin sheet of biocompatible materialbetween the bone defect and overlying soft tissue. Histologicalevaluation of animal tissues confirmed the hypothesis that if the moreaggressive and faster growing gingival epithelial cells were preventedfrom entering a periodontal bone defect during the healing phase, thennew cementum, bone, and periodontal ligament would be formed fromundifferentiated mesenchymal cells originating from the adjacent bone,cementum and bone marrow would selectively repopulate the defect.

At present, there is significant interest in the repair and regenerationof bony defects that may result from surgery such as the removal ofcysts, the removal of tooth roots, bone loss from infection orinflammatory process around teeth or dental implants, bone atrophy,trauma, tumors or congenital defects. Bone loss may result in pain, lossof function, mobility and subsequent loss of teeth, mobility andsubsequent loss of dental implants, and recurrent infections.Additionally, deficient bone volume precludes adequate prostheticreconstruction. Wound healing studies indicate that the most completehealing of oral and maxillofacial bone defects occurs when gingivalepithelial and connective tissue cells are prevented from entering thebony defect.

There are several commercially available products that have been usedsuccessfully as guided tissue regeneration membranes, including thosemade from expanded polytetrafluoroethylene (PTFE), high density PTFE,bovine type I collagen, polylactide/polyglycolide co-polymers, calciumsulfate and even human skin. A review of the scientific literatureindicates that no single ideal membrane material exists, but that eachtype of product has its own advantages and disadvantages.

An example of a current commercially available product employs alow-density expanded version of polytetrafluoroethylene (ePTFE) whichpresents a open-structure matrix to the gingival epithelial andconnective tissue cells. This expanded version of PTFE is characterizedby a low density of about 1.0 gm/cc or less and a porous, hydrophobicsurface. In spite of the hydrophobic surface, soft tissue cells readilyincorporate into the expanded matrix due to the open, porous structureof the material. While this connective tissue ingrowth is said toeffectively prevent the migration of epilthelial cells, it presents adifficult problem to the patient and surgeon in the later stages of theregenerative procedure. After several weeks to several months, thenon-absorbable low-density hydrophobic ePTFE barrier membrane must beremoved. The incorporated cells and fibrous connective tissue makeremoval painful and traumatic to the patient and very time-consuming forthe surgeon. The low-density open-matrix design of ePTFE devices alsoprovides a location for the ingress of food particles, bacteria, andother foreign bodies which, in turn, create post-operative problems withthe device such as inflammation, infection, wide exposure of the barriermaterial with wound dehiscence, and gingival recession. Any of thesecomplications may require early removal of the barrier material,therefore compromising the treatment outcome. Low-density open-matrix oropen-structure materials are generally soft and flimsy such that theywill not mechanically support tissue above the defect during normalfunctional activities within the mouth causing a breakdown of thebarrier's effectiveness. The articles described by Scantlebury, et. al.in U.S. Pat. Nos. 5,032,445 and 4,531,916 are such ePTFE devices.

Other products incorporate bio-absorbable polymer technology into theirdesign. Such products are made from dense collagen matrices of human orbovine origin, which are broken down via hydrolysis and absorbed intothe body fluids following several weeks to several months ofimplantation. While such devices eliminate the need for a secondsurgical procedure to remove them, some patients may exhibit a vigorousantigenic response to the devices which delays and often prevents thedesired healing process within the defect, and may cause dehiscence ofsutured wounds. Even in the absence of a specific antigenic response toimplanted collagen, breakdown and resorption of these devices oftenresults in generalized inflammatory cascade including neutrophil andmacrophage activation. This foreign-body response also producesundesirable effects with regard to healing kinetics and pain.Bio-resorption time also varies significantly from patient to patient,presenting both patient and surgeon with an uncertainty regardingoverall healing rate and pain management. Examples of collagen membranesin the literature are BioMend® and BioGide®. The articles described byLi in U.S. Pat. No. 5,206,028 and Geistlich in U.S. Pat. No. 5,837,278are examples of such devices.

Synthetic polymers of lactide, glycolide and their various copolymersare also used as guided tissue regeneration barriers. These materialsare biodegradable and offer the benefits of avoiding a surgicalprocedure for their removal. However, use of these materials results ininflammatory responses similar to those seen with naturally derivedpolymers such as collagen. In addition, the resorption profile may beunpredictable from patient to patient. These materials are also highlyporous which renders them susceptible to bacterial colonization andcontamination with foreign materials in the oral cavity in the event ofexposure. A synthetic membrane barrier exhibiting similarcharacteristics is Vicryl® (polyglactin) periodontal mesh, Resolute®periodontal membrane described by Hayes et al, in U.S. Pat. No.6,031,138 and Cytoplast® Resorb regenerative membrane.

Other products used as surgical membranes for the treatment of jaw andalveolar bone defects are human freeze-dried laminar bone and humanfreeze-dried dura mater obtained from human cadavers. These materialsare bio-absorbable and osteoconductive, but carry a small but unknownrisk of human disease transmission from donor to host. The risk ofdisease transmission precludes the use of this material by many surgeonsand patients.

In an effort to provide a material with the biocompatibility andchemical inertness of PTFE but without the disadvantages of the porousopen surface structure of expanded PTFE, a high density PTFE membranematerial has been used and has achieved widespread clinical acceptance.

In U.S. Pat. No. 5,957,690 and U.S. Pat. No. 6,019,764 the use of aflexible high-density polytetrafluoroethylene (PTFE) sheet material wasdisclosed as a material suitable for guided tissue regenerationprocedures. High density PTFE is substantially nonporous or microporousso as not to incorporate cells or attach to fibrous adhesions. Bypresenting a smooth surface to the biological materials, a high densityPTFE barrier is easily inserted and removed following extendedimplantation periods. A similar high density PTFE barrier material isdisclosed in U.S. Pat. No. 5,480,711. Examples of such products used forguided tissue regeneration include smooth and textured surface,hydrophobic high density PTFE such as Cytoplast®Regentex and TefGenFD®.

While high density PTFE medical barriers provide advantages overmacroporous barriers, the smooth surface of the high density PTFEbarriers sometimes leads to dehiscence of the soft tissue overlying thebarrier. The dehiscence problem is caused in part by the fact that thesmooth surface of high density PTFE will not incorporate cells and willnot attach to fibrous adhesions as compared to expanded PTFE.

An additional clinical problem exhibited by high density PTFE is relatedto its hydrophobicity, or tendency to repel water. The chemicalcomposition and resulting surface chemistry of a material determine itsinteraction with water. Hydrophobic materials have little or no tendencyto adsorb water and water tends to “bead” on their surfaces in discretedroplets. Hydrophobic materials possess low surface tension values andlack active groups in their surface chemistry for formation of“hydrogen-bonds” with water. In the natural state, PTFE exhibitshydrophobic characteristics, which requires surface modification torender it hydrophilic. All previously disclosed products, whetherconstructed from expanded PTFE or high density PTFE have suchhydrophobic characteristics.

It is well known in the art that biomaterial surfaces exhibitinghydrophobic characteristics are less attractive in terms of cellattachment. This is an advantage in some respects, as it prevents theready attachment and migration of certain bacteria into the intersticesof the material. However, in terms of interaction with host tissue, thischaracteristic may be less desirable and may contribute to dehiscence,or loss of soft tissue covering over the membrane during the course ofhealing. Dehiscence is a common clinical complication of guided tissueregeneration therapy, with an incidence of up to 60% according to thepublished literature. The clinical sequelae may indeed be serious,resulting in infection and failure of the procedure. The dehiscencephenomenon has been observed with both high density and expanded PTFEmembrane devices, both of which to date have only been available withhydrophobic surfaces.

Although there are no reports of hydrophilic PTFE used in theconstruction of guided tissue regeneration membranes or similarimplantable devices, hydrophilic, surface modified PTFE has a history ofuse as a filter in applications such as basic chemical and laboratoryfiltration, water purification, filtration of intravenous lines, bloodoxygenators and extracorporeal hemofiltration devices.

U.S. Pat. No. 5,282,965 relates to a hydrophilic porous fluorocarbonmembrane filter for liquids, which is used in microfiltration orultrafiltration of liquids such as chemicals and water, and to afiltering device using said membrane filter. The filter is treated withlow temperature plasma (glow discharge) to create a hydrophilic surface.Specifically this invention relates to a membrane filter for liquids,which is suitably used to filtrate chemicals for washing silicon wafersin semiconductor industries, and to a filtering device.

A hydrophilic semi-permeable PTFE membrane is disclosed in U.S. Pat. No.5,041,225. This invention describes hydrophilic, semi-permeablemembranes of PTFE and their manufacture, and further describes membranessuitable for use in body fluid diagnostic test strips and cell supportmembers. In this instance, the intent of the hydrophilic membrane is tocover the target area of a diagnostic test strip with a semi-permeablemembrane of a controlled pore size so that a fluid sample applied tosuch a membrane be applied in a controlled manner through the membraneto the underlying reagents. It should be noted that this inventiondiscloses an in-vitro device and does not mention or anticipate use as asurgical implant.

Hydrophilic polymer membranes have been developed for use in thepharmaceutical industry as disclosed in U.S. Pat. No. 5,573,668 whichdescribes a hydrophilic microporous membrane for drug delivery and amethod for its preparation. Hydrophilicity is achieved by theapplication of a thin hydrophilic polymer shell, where the shell doesnot substantially alter the complex geometry of the membrane. Typically,drug delivery devices of non-resorbable polymers such as described inthis patent are placed on the skin with adhesive, and are not surgicallyimplanted.

Hydrophilic polymer membranes, which are biocompatible,antithrombogenic, and incorporate functional groups for immobilizationof bioactive molecules are disclosed in U.S. Pat. No. 5,840,190.Specifically, this patent deals with membrane separators used inmachines involved in the extracorporeal circulation of blood such asheart-lung machine oxygenators, hemofiltration units of dialysismachines, invasive blood gas sensors and artificial organs such asartificial pancreas and skin.

There are two methods described in this patent for fabrication of thesesurface modified membranes. “Method A” describes preparation of acasting solution containing the membrane forming polymer and thenprecipitating the casting solution in a bath containing the surfacemodifying polymer. “Method B” describes preparation of the castingsolution containing the membrane forming polymer as well as the surfacemodifying polymer, and then precipitating the membrane from the castingsolution in a coagulation bath. While this method may work with manypolymers, including cellulose, cellulose acetate, polysulfone,polyamide, polyacrylonitrile, and polymethylmethacrylate, neither methodis feasible with PTFE. Further, there is no mention of PTFE within thetext or claims of this patent.

A method for coating a hydrophobic polymer so as to render said membranehydrophilic is disclosed in U.S. Pat. No. 4,525,374. This method is saidto be particularly for treating polypropylene or polytetrafluoroethylenein which the filter membrane is contemplated to have a pore size notlarger than two (2) microns. The treating solution has TriethanolamineDodecylbenzene Sulfonate (LAS) as the active ingredient. Treatment ofexpanded PTFE filters such as Poreflon® and GoreTex® are described inthe context of filters for various chemical fluids such as intravenousfluids. There is no disclosure of use of said devices as a medicalimplant or guided tissue regeneration membrane.

A number of challenges are encountered in the design of the ideal GTRbarrier. For example, the membrane must be dense enough to resistpassage of unwanted cells such as epithelial cells and bacteria, yet beable to allow the passage of biological fluids, oxygen and nutrientsrequired to sustain the viability of the regenerated tissue as well asthe overlying tissue. The porosity of currently available productsvaries widely, from fully dense to over 30 microns in average pore size.According to the literature, those with larger pore size typically havea higher infection rate in clinical use. In contrast, the fully densematerials, while exhibiting superior characteristics in terms ofinfection resistance, are criticized due to the concern that they areunable to conduct the passage of nutrients in an efficient manner. Thus,there is a need for an improved membrane material of sufficient densityto prevent the ingress of unwanted cells and bacteria, and yet be ableto readily allow passage of biological fluids, molecules and oxygen.

A second major design issue involves the surface macrogeometry. Thebarrier membrane must be smooth enough to achieve a high degree ofbiocompatibility, yet must integrate well with the surrounding tissue toachieve clinical stability. Current products, with the exception ofsmooth surface dense PTFE membranes, rely on a complex three-dimensionalsurface structure to facilitate such tissue integration. A highly poroussurface, while it is ideal for tissue ingrowth, presents problems withregard to bacterial contamination. An improved surface is needed whichwould encourage attachment of cells and tissues to achieve clinicalstability without sacrificing the advantages of a smooth surface.

It is thus advantageous to provide a barrier device of dense,hydrophilic PTFE which will provide for selective cell repopulation ofbone defects that does not allow the incorporation of cells or fibrousmaterials, has an improved hydrophilic surface for enhancement of cellattraction and attachment and for improved wetting by body fluids, iseasy to remove after extended implantation periods, will not provide alocation for contamination by foreign particles or bacteria, will notelicit a foreign-body inflammatory response, does not have the potentialto transmit human infectious disease, is soft and supple such thatcompliance is similar to soft tissues, will facilitate retention ofparticulate grafting materials, and is convenient to use.

SUMMARY

In accordance with some exemplary embodiments, the present inventionprovides a medical barrier that includes a sheet of hydrophilic,unsintered substantially unexpanded polytetrafluoroethylene (PTFE)polymer material having a density in a range of about 1.2 gm/cc to about2.3 gm/cc, and preferably in the range of about 1.45 gm/cc to about 1.55gm/cc, and having at least one textured surface. In one embodiment, thesheet has one textured surface and one substantially smooth surface, andhas substantially uniform strength in all directions.

The sheet of medical barrier of the present invention has a thickness ina range of about 0.125 mm to about 0.25 mm. Preferably, the texturedsurface is formed by a plurality of indentations formed in the surfaceof the sheet. The indentations have a depth less than the thickness ofthe sheet and each indentation has a nominal width of about 0.5 mm. Theindentations are distributed substantially uniformly over the surface ofthe sheet. In some embodiments, the indentations are distributed overthe surface of the sheet at about 196 indentations per squarecentimeter.

The medical barrier of the present invention is particularly welladapted for use in guided tissue regeneration in the repair of bonedefects, and particularly in the repair of alveolar bone defects. Thebarrier prevents the entry of rapidly migrating gingival tissue cellsinto the defect and allows the alveolar bone to regenerate. Duringhealing, the gingival tissue adheres somewhat to the textured surface ofthe barrier to anchor the gingival tissue over the barrier, therebypreventing dehiscence or splitting open of the tissue covering thematerial. However, the high density unexpanded substantially non-porousnature of the medical barrier of the present invention prevents gingivaltissue from growing into or through the barrier. Thus, after the bonedefect has healed, the barrier may be removed with a minimum of traumato the gingival tissue.

In contrast to hydrophobic PTFE, it has been found that hydrophilic PTFEmembranes exhibit a greater affinity for cellular adhesion, attachmentand spreading. In addition, with respect to bone cell interaction withbiomaterial surfaces, hydrophilic surfaces have been shown to promoteincreased mineralization and osteoblastic differentiation as measured byalkaline phosphatase (ALP) activity compared to hydrophobic surfaces.Transmission of body fluids, such as blood and plasma occurs morereadily with hydrophilic membranes. Clinically, this results in fasterand more predictable soft tissue coverage, improved soft tissueattachment without requiring ingrowth, and fewer wound healingcomplications when compared to similar devices manufactured fromhydrophobic PTFE. Thus, the present invention provides a significantclinical and biological advantage over current, hydrophobic PTFE guidedtissue regeneration membranes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the textured surface of the medicalbarrier of the present invention.

FIG. 2 is a perspective view showing the untextured surface of themedical barrier of the present invention.

FIG. 3 is an enlarged view of the textured surface of the medicalbarrier of the present invention.

FIG. 4 is a lateral cross-sectional view of a maxillary bony defectresulting from the extraction of a tooth.

FIG. 5 is a lateral cross-sectional view of the maxillary bony defect ofFIG. 4 showing the placement of the medical barrier of the presentinvention to cover the bony defect with the mucoperiosteal flap suturedover the medical barrier.

FIG. 6 is a lateral cross-sectional view showing the healed maxillarybony defect of FIG. 4 with the gingival tissue healed over the medicalbarrier of the present invention.

DETAILED DESCRIPTION

Referring now to the drawings, and first to FIGS. 1 and 2, a medicalbarrier according to one embodiment of the present invention isdesignated generally by the numeral 11. Barrier 11 comprises a sheet ofunsintered substantially unexpanded hydrophilic polytetrafluoroethylene(PTFE) polymer. As shown in FIG. 1, barrier 11 includes a texturedsurface 13, and as shown in FIG. 2, an untextured surface 15. Barrier 11has a density in the range of about 1.2 gm/cc to about 2.3 gm/cc, andpreferably in the range of about 1.45 gm/cc to about 1.55 gm/cc. Barrier11 has a sheet thickness in the range of about 0.125 mm to about 0.25mm. As shown in FIG. 3, the textured surface of the exemplary embodimentis formed by a plurality of indentations 15 formed in surface 13 ofbarrier 11. In some embodiments, indentations 15 may be hexagonal inshape, although other shapes are within the scope of the presentinvention. The indentations have a depth less than the thickness of thesheet, and in the illustrated embodiment indentations 15 are about 0.15mm deep. In some implementations, indentations 15 are about 0.5 mm wide.

Indentations 15 are distributed substantially uniformly over surface 13of barrier 11 at about 150 indentations per square centimeter to about250 indentations per square centimeter. In accordance with someexemplary implementations, indentations 15 are distributed over surface13 of sheet 11 at about 196 indentations per square centimeter.

The barrier of the present invention is made by first forming a thinsheet of unsintered PTFE and then embossing the sheet with indentations.PTFE resin is mixed with a lubricant such as mineral spirits to form apaste. The paste is then calendered in multiple passes between rollersto form a thin flat sheet of the desired thickness in the range of about0.125 mm to 0.25 mm. The calendering is performed multiple times inmultiple directions to reduce the thickness of the sheet and to impartsubstantially uniform strength in all directions to the sheet. Thelubricant is removed by drying the sheet at temperature somewhat abovethe boiling point of the mineral spirit lubricant, but well below thesintering temperature of PTFE, which is about 327 degrees C. Theforegoing process steps result in a flat sheet of unsintered PTFE about0.125 to 0.25 mm thick, having a density in the range of about 1.2 gm/ccto about 2.3 gm/cc, and having substantially uniform strength in alldirections. The resulting flat sheet has two substantially smoothsurfaces.

After the sheet has been dried, the sheet is embossed to form theindentations in one of its surfaces. In some embodiments, the embossingstep may be performed by placing a sheet of patterned polymer mesh ontop of the unembossed sheet of unsintered PTFE. The patterned polymersheet material, such as polyethylene or polypropylene, may be harder andhave more compressive strength than the unsintered PTFE material. Onesuch polymer sheet is embodied in a fine pore-size sheet filter materialmanufactured by Tetko, Switzerland. The polymer sheet has a pattern thatis embossed into the polymer sheet. The polymer sheet and the unsinteredPTFE sheet are passed together between a pair of rollers, which embossthe pattern of the polymer sheet into one surface of the unsintered PTFEsheet. After embossing, the polymer sheet may be discarded.

After embossing, the sheet may be treated by various methods known inthe art to impart hydrophilic characteristics to the membrane surface.These methods include the addition of a second polymer or hydrophilicchemical compound, chemical treatment of the membrane surface, laseretching or glow discharge plasma etching. The surface modified embossedunsintered PTFE sheet may be cut into smaller sheets of various shapeand size for packaging and distribution.

The surface modification to make the surface hydrophilic may be appliedselectively to the surface. For example, the hydrophilic portion of thesurface may be limited only to the central part 14 of the surface.Alternatively, the hydrophilic portion of the surface may be limited tothe marginal parts of the surface.

After surface modification, the membrane may be modified further bylinking the hydrophilic portion or portions to bioactive molecules,preferably by covalent bonds. Examples of such bioactive moleculesinclude growth factors, cytokines, morphogenetic proteins, cellattractants, adhesion molecules, and the like. The source of suchbioactive molecules may be autologous, allogenic, xenogenic orsynthetic.

Referring now to FIGS. 4-6, there is illustrated the manner of use ofthe barrier of the present invention. FIG. 4 is a lateralcross-sectional view of an adult human maxilla after a tooth extraction.The bone of the alveolar process is designated by the numeral 17. Softtissue gingiva 19 covers bone 17. A tooth socket is designate by thenumeral 21.

Socket 21 is an example of a bone defect. Other examples of bone defectsare those caused by periodontal disease, cyst formation, surgery, ortrauma. Normal healing of a defect includes migration of foreign cellssuch as fibroblasts and gingival epithelial cells. As the cellsproliferate into the defect, they inhibit bone cell regeneration, whichresults in overall loss of bone mass. In the case of extractions, theloss of bone mass results in a loss of alveolar ridge profile.

Referring now to FIG. 5, there is shown one method of using the barrierof the present invention. Socket 19 is shown packed with granularparticles of hydroxyapatite as a precursor to bone. Those skilled in theart will recognize that other materials or articles, such asendoseouss-type dental implants, may be placed into socket 21. Thepacked socket 21 is covered with a layer 23 of the barrier of thepresent invention. The smooth side of the barrier is placed over socket21 and bone 17. Thus, the textured of the barrier is positioned adjacentthe gingival tissue 19. The substantially uniform strength in alldirections of the material of the present invention allows the surgeonto shape layer 23 over socket 21 and bone 17. After layer 23 is placedover socket 21 and bone 17, the gingival flaps 19 are sutured over layer23. Layer 23 holds the hydroxy apatite particles in place in socket 21during healing and prevents migration of cells and connective tissueinto socket 21. However, connective tissue forms a weak attachment withthe textured surface of layer 23, without growing through the material.The attachment is weak enough that the layer may be removed afterhealing without significant trauma but is strong enough to prevent thedehiscence.

Referring to FIG. 6, there is shown the extraction site after healing,but prior to removal of layer 23. As shown in FIG. 6, the alveolar ridgeprofile 25 is preserved and the gingival tissue 19 is completely healedover ridge 25. Layer 23 may be removed by making a small incision (notshown) in gingival tissue 19 to expose a portion of layer 23. The layer23 may then be pulled out with forceps or the like. Since the connectivetissue attaches only weakly to the hydrophilic textured surface of thematerial of the present invention, the material may be pulled out easilyand without trauma to the patient.

From the foregoing, it may be seen that the medical barrier of thepresent invention overcomes the shortcomings of the prior art, and isparticularly well adapted for use in guided tissue regeneration in therepair of bone defects, as for example in the repair of alveolar bonedefects. The barrier prevents the entry of rapidly migrating gingivaltissue cells into the defect and allows the alveolar bone to regenerate.During healing, the gingival tissue adheres somewhat to the hydrophilictextured surface of the barrier to anchor the gingival tissue over thebarrier, thereby preventing dehiscence or splitting open of the tissuecovering the material. However, the high density unexpandedsubstantially non-porous nature of the medical barrier of the presentinvention prevents gingival tissue from growing into or through thebarrier. Thus, after the bone defect has healed, the barrier may beremoved with a minimum of trauma to the gingival tissue.

Aspects of the present invention have been illustrated and described indetail with reference to particular embodiments by way of example only,and not by way of limitation. It will be appreciated that variousmodifications and alterations may be made to the exemplary embodimentswithout departing from the scope and contemplation of the presentdisclosure. It is intended, therefore, that the invention be consideredas limited only by the scope of the appended claims.

What is claimed is:
 1. A guided tissue regeneration membrane comprisinga multi-surfaced polytetrafluoroethylene sheet having a portion of onesurface of the polytetrafluoroethylene sheet that is hydrophilic, whichrenders the membrane surface substantially compatible with water, bodyfluids, blood and aqueous solutions, wherein the hydrophilic portion islimited to a central portion of the membrane and comprises an embossedportion, wherein embossments of the hydrophilic portion are etched byone or more of glow discharge plasma and a laser.
 2. A medical barriercomprising a multi-surfaced membrane, wherein the membrane comprises asheet of high density, unexpanded, unsintered polytetrafluoroethylene,wherein one surface of the membrane is embossed and treated, afterembossing, by addition of one or more of a polymer, a reactive chemical,and an etching of the surface, thereby providing a limited portion ofthe one surface that is compatible with one or more fluids, and whereinthe medical barrier is adaptable for use in guided tissue regenerationin the repair of bone defects.
 3. The medical barrier of claim 2,wherein the limited portion of the one surface is substantiallycompatible with water.
 4. The medical barrier of claim 2, wherein thelimited portion of the one surface is substantially compatible with bodyfluids.
 5. The medical barrier of claim 2, wherein the limited portionof the one surface is substantially compatible with blood.
 6. Themedical barrier of claim 2, wherein the limited portion of the onesurface is substantially compatible with water, body fluids, blood andaqueous solutions.
 7. The medical barrier of claim 6, wherein theembossed portion is treated with at least one of a hydrophilic polymerand a reactive chemical.
 8. The medical barrier of claim 7, wherein theembossed portion is linked via covalent bonds to bioactive molecules. 9.The medical barrier of claim 8, wherein the bioactive molecules includeone or more of a growth factor, a cytokine, morphogenetic protein, acell attractant, and an adhesion molecule.
 10. The medical barrier ofclaim 9, wherein the source of the bioactive molecules is selected fromthe group consisting of autologous, allogenic, xenogenic and synthetic.11. A tissue regeneration membrane usable as a medical barrier andcomprising a high density polytetrafluoroethylene sheet having aplurality of surfaces, wherein the membrane comprises high density,unexpanded, unsintered PTFE, wherein an embossment of a selected portionof one of the plurality of surfaces is treated by one or more of polymercoating, a chemical reaction, and an etching, thereby making theselected portion of the one surface hydrophilic and substantiallycompatible with water, body fluids, blood and aqueous solutions, andwherein the medical barrier provides for guided tissue regeneration. 12.The tissue regeneration membrane of claim 11, wherein medical barrier isadapted for use in the repair of bone defects.
 13. The tissueregeneration membrane of claim 11, wherein the selected portion of theone surface includes an embossed portion treated with a hydrophilicpolymer.
 14. The tissue regeneration membrane of claim 11, wherein theselected portion of the one surface is treated by chemical reaction. 15.The tissue regeneration membrane of claim 11, wherein the selectedportion of the one surface is treated by etching.
 16. The tissueregeneration membrane of claim 15, wherein one of the plurality ofsurfaces is textured and wherein another of the plurality of surfaces issubstantially smooth.
 17. The tissue regeneration membrane of claim 11,wherein the selected portion is provided at the periphery of themembrane and comprises a border of the membrane.
 18. The tissueregeneration membrane of claim 11, wherein the selected portion islimited to a central portion of the membrane.
 19. The medical barrier ofclaim 2, wherein the embossed portion is treated with a hydrophilicchemical.
 20. The medical barrier of claim 2, wherein the embossedportion is laser etched.
 21. The medical barrier of claim 2, wherein theembossed portion is etched by glow discharge plasma.